"The density of moist air may be determined by a similar relation: D = 1.2929 (273.13/T) [(B – 0.3783e)/760] where T is the absolute temperature; B, the barometric pressure in mm, and e the vapor pressure of the moisture in the air in mm."

"The density of air at sea level is approximately 1/800th the density of water."

1.25 kg/m3

Density (D) is the mass of a given volume of a substance. Density can be
obtained by dividing the mass (m) of an object by the volume of that object …

D = m/V

A mass that is concentrated in a small volume has a greater density
than a substance of equal mass that occupies a larger volume. Thus, gases
have the smallest densities
as compared to solids and liquids because gas molecules contain mostly empty space
while molecules in liquids are more tightly packed together.

The density of a substance (mainly gases) depends on temperature and pressure.
Gases are usually compared at a standard temperature and standard pressure. These
are the freezing point (0 °C) and normal air pressure at sea level (760 torr), respectively.

The density of dry air at sea level is 1.2929 kg/m3 or about
1/800th the density of water. But as altitude increases, the density drops
dramatically. This is because the density of air is proportional to the
pressure and inversely proportional to temperature. And the higher you go into the atmosphere, the
lower the pressure gets. Pressure is approximately halved for each additional
increase of 56 km in altitude. To determine the density of dry air at a given altitude
we could use the relation

D = D0 × (T0/T) × (P/P0)

Where D0 is the known density at absolute temperature T0 and pressure P0
and D, the unknown density at absolute temperature T and pressure P.

Just as there is a density of dry air, there is also the density of moist
air, or air that contains moisture (humidity). To obtain this density
you can use the relation

D × (273.15/T) × [(B–0.3783 e)/760]

Where

D is the density of dry air at sea level,T is the absolute temperature in kelvin,B is the barometric pressure in torr, ande is the vapor pressure of the moisture in the air in torr.

"Another way to estimate the density of air is through its composition; i.e., roughly 78% nitrogen, 21% oxygen and 1% argon. With respective molar masses for those gases being 28, 32 and 40 g/mol, the average molar mass of air is therefore:0.78 × 28 + 0.21 × 32 + 0.01 × 40 = 28.96At 0 °C and normal sea level pressure a mole of gas occupies 22.4 liters, so a cubic meter of air has a mass of:1000/22.4 × 0.02896 = 1.293 kg."